In normal breathing, the muscles of the rib cage and diaphragm contract, increasing the size of the chest cavity. The lungs inflate because of the negative pressure that is created in the lungs as the chest volume increases. This causes air to flow into the lungs. When the diaphram and rib cage relax, decreasing the size of the chest cavity, the air is passively expelled from the lungs. The lungs are prevented from collapsing by a negative pressure which exists in the pleural space, that is the potential space between the parietal and visceral pleuras.
When the chest wall sustains a penetrating wound as from a gun shot or knife, the wound opening creates a path for outside air to flow into the chest cavity. This flow of external atmospheric air into the chest cavity eliminates the negative pressure which normally exists in the pleural space. As a result, the lungs cannot inflate properly, because the chest defect allows the air which has been drawn into the chest cavity to equalize the pressure therein with the atmospheric pressure. The presence of the atmospheric air in the chest may also introduce contaminates into the chest cavity.
At the present time, one of the treatment procedures is to provide an occlusive dressing large enough to overlap the wounds' edges and to tape it securely on all four sides so as to seal the wound and prevent air from passing into the chest cavity through the wound. This permits the patient to breath without building up pressure within the cavity unless the lung has been punctured or torn. If the lung has been penetrated, air will be drawn into the chest cavity through that penetration and produce a pressure build-up within the chest cavity if the wound has been sealed externally. In order to overcome this problem under the emergency conditions in the field, the American College of Surgeons recommends the taping of the occlusive dressing on only three sides so that if pressure is building up within the chest cavity, this pressure may be discharged through the open side of the dressing. Unfortunately, however, the conditions surrounding the emergency treatment of the patient may neutralize the valve effect of this type of dressing application. These conditions include the application of a spine board, other pressure dressings, cot-restraint belts and the specific location of the wounds relative to the patient's position during transport. Frequently, the patient also will have to be moved into a position, or external restraining or support apparatus applied to the patient which will interfere with the operation of the valve effect of the open side of the dressing.
The problem for the emergency staff during the early treatment of such wounds is to monitor the patient and prevent, if possible, the build-up of pressure within the chest cavity, even when one of the lungs has been penetrated. This is an extremely difficult problem to solve when there are a great many other demands on the attendant. Frequently, it is necessary to use a pressurized oxygen device to force uninjured lungs to inflate. This device, however, has the potential of increasing the damage to an injured lung by forcing high pressure air through the opening or defect in that lung. This pressurization through the lungs may further increase the pressure in the chest cavity if the chest opening or defect is sealed.
One of the most important life threatening conditions that must be prevented is sufficient build up of pressure within the chest cavity making it impossible for the lung to inflate, thus collapsing the lung. This pressurized condition within the chest cavity also compresses the heart and reduces its ability to function. This invention provides a valve controlled release opening to prevent this pressure build up in the chest cavity.